In a known clamping device of this kind (West German patent application 1 283 168), one end of the clamping sleeve is provided with a hollow spindle which in turn engages in the internal thread of the vise housing. The hollow spindle has a diameter less than the outside diameter of the clamping sleeve. The clamping sleeve and the hollow spindle are rotatable relative to the housing through more than 180.degree. by means of a crank handle which engages the abutment. The hollow spindle is supported by its free end on one end of the clamping slide of a machine vise. This clamping slide comprises at its other end a driver plate which engages by a corresponding opening in an annular groove of the hollow spindle. In order for the plunger to be able to perform its clamping stroke, there must be sufficient axial play between the driver plate and the annular groove. This known clamping device has various drawbacks. It has a relatively long overall axial length, which is due to the fact that the hollow spindle is provided adjacent to the clamping sleeve, and that furthermore between the clamping sleeve and the thread of the hollow spindle there must be space for the annular groove and the driver plate. As the diameter of the hollow spindle is less than that of the bearing bush, when an ordinary self-locking thread is used it has only a relatively low pitch. This is a particular disadvantage during quick-action clamping of workpieces. During quick-action clamping of workpieces, several workpieces of the same size are clamped successively in a machine vise or other apparatus. For this, it is necessary to move the movable jaw about 2-4 mm away from the workpiece, so that the workpiece can be placed in the vise or clamping device conveniently. In order to achieve the desired feed or opening stroke of 4 mm, at least half a turn of the crank handle is required. Added to this, however, is another angle of rotation of the crank handle, which is needed after the clamping slide has come into contact with the workpiece in order to turn the abutment relative to the clamping member, to move the studs in the process out of their position at an angle to the clamping sleeve axis, into an approximately parallel position or slightly beyond the dead center position. Here too, the play required between annular groove and driver plate becomes apparent as a disadvantage. For the fact is that the hollow spindle must be moved at each feed stroke by rotation so far away from the driver plate that there is sufficient play between driver plate and annular groove, and movement of the clamping slide during the clamping stroke is not impeded. To perform the feed stroke and the clamping stroke and, conversely, to open the clamping device, nearly one full turn of the crank handle is required. During quick-action clamping of workpieces, however, the angle of rotation of the operating lever should be as small as possible, and on no account exceed 180.degree.. Another drawback of the known clamping device lies in that the clamping pressure cannot be adjusted exactly. To adjust the clamping pressure, at the abutment end of the clamping sleeve there is of course provided an adjusting sleeve which comprises a stop face for a stop pin connected to the abutment. Another stop face is provided on the bearing bush. The adjusting sleeve can be latched by means of serrations in various rotational positions relative to the clamping sleeve, so that the distance between the two stop faces and hence also the maximum angle of rotation of the abutment can be adjusted. But the clamping force can be adjusted only very coarsely by limiting the angle of rotation. If, after the end of the clamping stroke, the workpiece yields slightly, then the clamping force drops immediately and the workpiece is no longer held securely enough. In addition to these disadvantages, the known clamping device has the further disadvantage that the bearing bush can rotate through more than 360.degree.. Consequently, the angular range within which the crank handle must be moved to perform the feed and clamping strokes may be repeatedly in a different range, referred to one full turn of the crank handle.
It is therefore the object of the invention, on the basis of a clamping device of the kind mentioned hereinbefore, to provide a quick-action clamping device which is suitable for quick-action clamping of workpieces and the like and at the same time has a short overall axial length, which requires only a small angle of rotation of the operating lever within a predetermined angular range to perform the feed and clamping strokes or the opening stroke, and in which the clamping pressure can be adjusted easily and precisely and is maintained even in case of yielding of the workpiece.
According to the invention, this is achieved by the fact that
(a) the external thread is provided directly on the outer circumference of the clamping sleeve, concentrically to the region of the clamping member and the studs, PA1 (b) the compression spring is supported at one end on the housing and at the other end on the plunger, and acts via the latter on the clamping member, PA1 (c) the adjusting sleeve is axially displaceable relative to the clamping sleeve by means of a fine thread, and several cup springs are disposed between the side of the abutment facing away from the studs and the adjusting sleeve, and PA1 (d) rotational movement of the clamping sleeve relative to the housing is limited by stop faces in the direction of opening.
Arrangement of the external thread on the outer circumference of the clamping sleeve has two important functions. Firstly, the overall axial length of the clamping device is shortened thereby and its structure simplified. Secondly, the external thread has a relatively large diameter, so that the external thread can have a relatively large pitch, and yet self-locking is still guaranteed. The large pitch has the advantage that the desired opening stroke of 2-4 mm is achieved with a relatively small angle of rotation. For example, with a total angle of rotation of the operating lever of 120.degree., which includes the angular movement required to perform the clamping stroke, a feed or opening stroke of over 3 mm can be achieved. As the compression spring is supported on the plunger, it likewise has two functions: it biases the plunger into its open position during the opening stroke. The clamping slide can therefore be rigidly connected to the plunger, and it is not necessary to provide axial play. This too reduces the angle of rotation of the operating lever. By means of the adjusting sleeve, which is axially displaceable relative to the clamping sleeve, the bias of the cup springs can easily be altered and hence the clamping pressure can be adjusted precisely according to a scale. The resilient mounting of the abutment on the cup springs furthermore has the advantage that in case of yielding of the workpiece, the clamping pressure is maintained.